Finally, empirical data suggests that assets are sold much more slowly during retirement years than when they are accumulated during working years. - Didier Sornette

The assumption of perfectly rational, maximizing behavior won out until recently in the art of modeling, not because it often reflects reality, but because it was useful.

According to the academic world view that markets are efficient, only the revelation of a dramatic piece of information can cause a crash, yet in reality even the most thorough post-mortem analyses are typically inconclusive as to what this piece of information might have been. For traders and investors, the fear of a crash is a perpetual source of stress, and the onset of the event itself always ruins the lives of some of them.

The same basic ingredients are found repeatably: fueled by initially well founded economic fundamentals, investors develop a self-fulfilling enthusiasm by an imitative process or crowd behavior that leads to an unsustainable accelerating overvaluation.